Tandem Mass Spectrometry-Based Method

It should be recognized that at least two criteria should be considered in selection of the internal standards in this approach  

In this approach, the specific PIS or NLS to a lipid class is acquired in the profile mode with a stable ion current for a certain time period (commonly a few 

As aforementioned, the peak intensities of the fragment ions depend on the chemical structures (i.e., the number of carbon atoms, and the number and location of double bonds) of each individual species of the class in addition to the conditions for CID. This is because the intense fragment ions represent those thermodynamically stable ions or because these fragment ions produced are favored in dissociation kinetics, both of which depend on the chemical structures (i.e., the number of carbon atoms, and the number and location of double bonds) of individual species of the class. The presence of this species-dependent process was demonstrated in a very early study reporting such a method [22] and confirmed in other studies [23, 29]. 

For example, a tandem MS analysis through PIS of mIz 184 was performed for analysis of PC species present in a lipid extract of Chinese hamster ovary cells in which an equimolar mixture of four PC species was used as internal standards [22]. Since this fragment ion represents the protonated phosphocholine under experimental conditions, the PIS detects all the protonated choline-containing GPL species in the solution. However, the spectrum clearly showed the decreases in the ion peak intensities of these internal standards as their molecular weights increased. A calibration curve from the ion peak intensities of the standards was derived and used to correct the experimental ion abundances to quantify individual PC species in this approach [22]. Accordingly, a built-in (non)linear calibration curve from two or more internal standards can be determined from their peak intensities. The concentration of each species of the class can then be derived from its ion peak intensity of the tandem MS mass spectrum by comparison with the calibration curve. 

The authors of the paper pointed out that the net effect of the molecular weight on signal intensity is the sum of the following physical phenomena [22]  

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Macek et al. [120] developed a method to quantitate omeprazole in human plasma using liquid chromatography-tandem mass spectrometry. The method is based on the protein precipitation with acetonitrile and a reversed-phase liquid chromatography performed on an octadecylsilica column (55 x 2 mm, 3 /im). The mobile phase consisted of methanol-10 mM ammonium acetate (60 40). Omeprazole and the internal standard, flunitra-zepam, elute at 0.80 0.1 min with a total rim time 1.35 min. Quantification was through positive-ion made and selected reaction monitoring mode at m/z 346.1 —> 197.9 for omeprazole and m/z 314 —> 268 for flunitrazepam, respectively. The lower limit of quantification was 1.2 ng/ml using 0.25 ml of plasma and linearity was observed from 1.2 to 1200 ng/ml. The method was applied to the analysis of samples from a pharmacokinetic study. 

Yu S, Li S, Yang H, Lee F, Wu JT, Qian MG. A novel liquid chromatography/tandem mass spectrometry based depletion method for measuring red blood cell partitioning of pharmaceutical compounds in drug discovery. Rapid Commun Mass Spectrom 2005b 19(2) 250-254. 

Isotope-coded affinity tag (ICAT) peptide labeling is an approach that combines accurate quantification and concurrent sequence identification of individual proteins in complex mixtures (Gygi, et al 1999). This method is based on a newly synthesized class of chemical reagents used in combination with tandem mass spectrometry. The method consists of four steps ... 

Gros M, Petrovic M, Barcelo D (2006) Development of a multi-residue analytical method based on liquid chromatography-tandem mass spectrometry (LC-MS-MS) for screening and trace level determination of pharmaceuticals in surface and wastewaters. Talanta 70 (4) 678-690... 

The analyses of illicit drugs and metabolites in the sampled waters were performed following a previously described and validated fully automated method based on on-line solid phase extraction-liquid chromatography-tandem mass spectrometry (on-line SPE-LC-MS/MS) [19]. 

Sabatini, L., Barbieri, A., Tosi, M., Roda, A., and Violante, F. S., A method for routine quantitation of urinary 8-hydroxy-2 -deoxyguanosine based on solid-phase extraction and micro-high-performance hquid chromatography/electrospray ionization tandem mass spectrometry, Rapid Communications in Mass Spectrometry 19(2), 147-152, 2005. 

Smalley, J., Kadiyala, P., Xin, B., Balimane, P., and Olah, T. (2006). Development of an online extraction turbulent-flow chromatography tandem mass spectrometry method for cassette analysis of Caco-2 cell based bi-directional assay samples. J. Chromatogr. B Ana. Technol. Biomed. Life Sci. 830 270-277. 

A critical review of the inherent limitations of modern PFA analytical methods is available in Martin et al. [18], but some examples are discussed here. For quantitative determination, the HPLC system is often interfaced to a Micromass or Sciex tandem mass spectrometer operated in the negative ion electrospray mode. Instrumental parameters are optimized to transmit the [M - H] ion for all analytes (Table 5). When possible, multiple daughter ions are monitored, but quantitation is generally based on a single product ion (Table 5, Fig. 4). In the electrospray tandem mass spectrometry (ES MS/MS) system, the 499 Da -> 80 Da transition can provide a stronger signal than... 

Fig. 5 Statistical evaluation of LC-MS-based methods for tropane alkaloids referred in this chapter. (a) Relative frequency of ionization methods. +APCI positive atmospheric pressure chemical ionization, +ESI positive electrospray ionization, FAB fast atom bombardment, +TSP positive thermospray, (b) Relative frequency of scan modes used. MS full scan MS, MS/MS tandem mass spectrometry (product ion scan), MRM multiple reaction monitoring, SIM selected ion monitoring, (c) Relative frequency of mass analysers used. EBQtQ2 double focusing sector field mass spectrometer, IT ion trap, QqQ triple quadrupole, SQ single quadrupole. Considered publications were found by PubMed data-based search and references cited in these articles...

For proton affinity determination, the kinetic method involves the formation of the proton bound heterodimer between the two bases whose affinities are to be compared. By tandem mass spectrometry, the appropriate cluster ion [BiHB2]+ is selected and its spontaneous or collisional dissociation is observed. As shown in Figure 4.16, the competitive dissociation leading to the two protonated monomers is analysed and the relative abundances of the monomers [BiH]+ and [B2H]+ are measured. From these abundances, the relative proton affinities of the two bases Bi and B2 can be calculated and the proton affinity of one of the two bases can be determined, if the proton affinity of the other is known. 

Determination of oxidized amino acids in urine is usually performed by isotope dilution gas chromatography-mass spectrometry (L9). DOPA is estimated by HPLC separation of acid protein hydrolysates with fluorescence detection (excitation 280 nm, emission at 320 nm) (A15). Other methods are based on borate-hydrochloric acid difference spectroscopy (this method suffers interference from tyrosine and tryptophan) (W2), derivatization of DOPA with nitrite and subsequent coulometric determination (W3), and fluorometric detection after derivatization with ethylenediamine (A15). 3-Hydroxylysine is quantitated by HPLC with 9-fluorenylmethyl chloroformate precolumn derivatization (M25) of amino acids obtained by gas-phase hydrolysis of proteins (F21). Other general methods to detect amino acid damage are mass spectometry methods applied to protein hydrolysates, such as tandem mass spectrometry (F6). 

There have been a few reports in the literature where hair has been analyzed directly for cocaine analytes, without analyte isolation. The earliest report was by Valente et al., who compared direct incubation of hair with the antiserum in an RIA test with acid, base, and methanol isolation. Although cocaine analytes were detected using this method, only 31% were recovered. In 1993, Kid well and Welch etal. noted that cocaine analytes could be observed in hair using tandem mass spectrometry (MS/MS) with no prior isolation. The washed samples were rapidly heated and the vaporized material analyzed. However, Welch et al. report that unambiguous results were only obtained when the hair samples were cryogenically powdered, which required more effort than preisolation of the analytes. 

Calbiani, F. et al. Validation of an ion-pair hquid chromatography-electrospray-tandem mass spectrometry method for the determination of heterocychc aromatic amines in meat-based infant foods. FoodAddit. Contam. 2007, 24, 833-841. 

Gentili, A. Caretti, F. 2011. Evaluation of a method based on liquid chromatography-diode array detector-tandem mass spectrometry for a rapid and comprehensive characterization of the fat-soluble vitamin and carotenoid profile of selected plant foods. J. Chromatogr. A. 1218 684-697. 

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